Pump

ABSTRACT

An improved pump construction may be achieved by forming one or more of the major components of the pump from sintered metal. A two-stage rotary vane-type vacuum pump, for example, may advantageously employ sintered metal stators, rotors, vanes, and end plates and sintered metal separator plate. Moreover, an inherently &#39;&#39;&#39;&#39;leaky&#39;&#39;&#39;&#39; valve may be provided for the outlet of the second stage of the pump by placing a resiliently mounted, normally closed sintered metal valve plate over the outlet.

United States Patent [72] Inventor Joseph A. LeBlanc, .lr.

Chicago, 1111. [21] App1.No. 835.132 {22] Filed June 20, 1969 [45] Patented Nov. 23, 1971 [73] Assignee Precision Scientific Co.

Chicago, Ill.

[54] PUMP 10 Claims, 7 Drawing Figs.

[52] US. Cl 418/96, 418/179 [51] Int. Cl F041 11/00, F04f 5/46 [50] Field of Search 103/126 M, 216 M;4l8/179, 90, 96; 137/513.3; 92/153; 308/D1G. 5

[56] References Cited UNITED STATES PATENTS 2,853,159 9/1958 Kuhn 137/513.3

3,040,973 6/1962 Wessling 418/13 3,460,481 8/1969 White 103/126 M 2,869,514 l/l959 Gluss 92/153 X 2,907,304 10/1959 Macks 92/153 X 3,109,684 11/1963 Tupper 308/D1G. 5

Primary Examiner-Carlton R. Croyle Assistant E.ran1iner Richard E. GluCk Auorneys- Ronald L. Engel, Daniel W. Vittum, .lr., Gomer W. Walters and John A. Waters ABSTRACT: An improved pump construction may be achieved by forming one or more of the major components of the pump from sintered metal. A two-stage rotary vane-type vacuum pump, for example, may advantageously employ sintered metal stators, rotors, vanes, and end plates and sintered metal separator plate. Moreover, an inherently leaky valve may be provided for the outlet of the second stage of the pump by placing a resiliently mounted, normally closed sintered metal valve plate over the outlet.

PATENTEDN V 2 I 3,622,254

SHEET 3 OF 3 INVENTOR.

Jas /l /4,, [651mm JR PUMI BACKGROUND OF THE INVENTION 1. Field ofthe Invention This invention relates generally to pumps and more particularly to mechanical vacuum pumps in which the major components of the pumps are formed of sintered metal.

2. Description of the Prior Art Vacuum pumps may be of the reciprocal piston type, wherein a piston draws gas into a cylindrical chamber through an inlet and expels gas from the chamber through an outlet, or they may be of the rotary internal vane Gaede-type pumps, such as the one shown in U.S. Pat. No. 3,040,973 issued June 26, I967 in the name of K. F. Wessling. The Wessling pump is a two-stage vacuum pump, with each stage comprising a stator with a rotor eccentrically mounted therein. Slidable vanes ride in radial grooves in the rotor, so that they bear against the inner wall of the stator and form a seal between the stator and the rotor. An inlet and an outlet are provided in the interior portion of each stator, so that the rotation of the rotor will draw gas into the inlet and expel gas through the outlet of the stator. The two stages of the Wessling pump are mounted sideby-side, separated by a separator plate and mounted in a hollow casing. An end plate caps one end of the pump unit assembly and an intake manifold or trap assembly is provided at the other end of the pump unit assembly and provides an inlet therefor.

The major components of both reciprocal piston pumps and rotary vane type pumps are customarily constructed from metal castings, primarily cast iron or cast aluminum. These metal castings are not entirely satisfactory, however, as they are heavy and expensive and require a substantial amount of machining in order to obtain proper tolerances for moving parts.

Another disadvantage in the metal castings is especially apparent in the rotary vane type pump. In such a pump, in order to effect a seal between the stator and the vanes, the ends of the vanes bearing against the stator gradually wear down and seat" with the irregularities in the stator surfaces. To this end, it would be desirable that the vanes be formed from a softer metal than the stator, so that the inexpensive and easily replaceable vanes will wear down, rather than the more expensive and more difficult to replace stator. However, with cast metals it is often somewhat difficult to obtain the proper relative hardness between vanes and stator, and the heat treating required to obtain the different hardness properties is an expensive and not altogether reliable process.

It is therefore a primary object of the present invention to provide a more suitable material for the construction of pump parts.

Naturally, both types of the above-described pumps require internal lubrication for all moving pans. In the rotary vane type pump, for instance, oil must be provided between the ends of the vanes and the stator in order to minimize friction and to effect a seal between the parts.

Rotary vane type pumps are generally lubricated in one of two ways. In the type of pump known as a dry" pump, such as the one described in U.S. Pat. No. 2,558,837, issued July 3, 1951, in the name of .l. R. Frei, an external oil reservoir provides oil to the system through a tube to a felt disc or some other absorbent material adjacent to the compression chamber. The oil then seeps into the compression chamber through the wall via a hole in the wall that may be either open or may be filled with a porous material such as sintered bronze or the like. In such pumps, the oil supply provides only a small quantity of oil to the interior portion of the pump, but this small quantity ofoil is adequate for the operation of the pump.

The other principal type of rotary vane type pump is exemplified by the above-identified Wessling patent. In that pump, a hollow casing surrounds the pump units and this casing is completely tilled with oil or some other suitable lubricant, thereby completely immersing the pump units. The interior portions of the two stage Wessling pump are lubricated by means of a leaky valve covering the exhaust outlet port of the secondary stage of the pump. This type of valve permits oil to seep into the compression chamber when the pressure in the chamber is below the pressure outside the chamber. Conversely, excess oil in the chamber is flushed out of the chamber by the sweeping vanes when the compression stroke creates a pressure in the chamber greater than the pressure outside the chamber. Oil seeping into the secondary stage of the pump through the outlet also lubricates the primary stage of the pump by passing through an opening in the separator plate between the two stages. Of course, the oil bath in the Wessling pump also serves a sealing function as well.

The simplicity of the Wessling pump provides many advantages over the dry" pump, but the Wessling type of pump is still deficient in many respects. First, the leaky valve covering the outlet of the secondary stage of the pump is complex, noisy, expensive, and requires close tolerances in order to obtain the proper rate of oil flow. Moreover, a relatively large quantity of oil seeps into the pump on every cycle so that there will be sufficient oil to seep through the opening in the separator plate to the primary state, and this impairs the performance of the pump because the oil tends to occlude gas. Moreover, the pump requires additional power to flush out this additional oil on every cycle. Furthermore, lubricating the primary stage merely by having an opening in the separator plate can result in sufficient oil passing to the intake stage and this could cause excess wear and burning of the elements in the intake stage.

Therefore, another object of the present invention is to provide a pump that adequately supplies lubricant for all moving parts and provides only the quantity of oil required for the operation of the pump (as in the dry" pump) yet functions with the simplicity of the type of lubrication system shown in the Wessling pump.

A further object of the present invention is to provide an improved outlet valve for the exhaust of a mechanical vacuum pump.

The foregoing and other objects, advantages, and features may be obtained by constructing one or more of the major components of a mechanical vacuum pump from sintered metal, rather than from the cast metals heretofore employed.

Previously, sintered metal parts have been employed for rather limited purposes and generally only for small parts, because sintered metal has always been considered to lack adequate tensile strength and ductility for use in major construction components. The above-identified Frei patent, for example, discloses the use of sintered metal rings on a rotor element in order to provide a lubrication passageway from an oil reservoir outside the pump unit to the internal parts of the unit. Frei, however, employs conventional cast iron parts for all of the major components of his vacuum pump and used soft sintered bronze rings merely as lubricating passageways and not in a manner that involves any structural function for the part.

Likewise, Knudson US Pat. No. 2,487,449, issued Nov. 8, 1949 discloses the use of a porous metal sleeve similar to the one described by Frei for lubricating the interior portions of the rotary vane type pump. Again, however, Knudson employs conventional cast iron parts for all of the major components of his pump and uses the soft sintered bronze sleeves only for lubricating purposes and not for any structural requirements. The use by Frei and Knudson of sintered metal lubricating passageways in a rotary vane type pump is very similar to the more common usage of sintered metal, namely, as bushings for rotating shafts. A sintered metal bushing is advantageous because lubricant can be applied to the outside of the bushing, and it will seep through the porous bushing to the friction surface on the inside of the bushing without requiring any separate channels or passageways.

In accordance with the present invention, it has been found that major components of a mechanical vacuum pump, as well as such minor components as bushings, sleeves. and rings, may be constructed entirely from sintered metal, and the resulting pump provides numerous advantages over the cast iron or cast aluminum pumps heretofore known. Sintered metal parts (i.e., parts produced by applying a combination of pressure and heat to powdered metal in a die) are lighter than standard cast metal parts and require little or no machining. If sintered metal parts are used for all the major components of a rotary vane type vacuum pump, namely, stators, rotors, vanes, end plate, and center plate, the resulting pump unit can cost as little as 25 percent of the cost of the same unit manufactured from cast metal parts.

Additionally, such parts possess a natural porosity and this enables lubricants to pass directly through the metal without requiring extra boring or machining steps in order to provide oil channels therein. If porosity is not desired, a sintered metal part can be sealed easily by impregnating the part with a plastic resin of another metal. This inherent porosity provides yet another major advantage over standard cast metal parts in pumps for pumping gases, especially in the type of pump described in the Wessling patent. With stators and end plates manufactured from sintered metal and the entire pumping unit immersed in oil, the pressure differential between the atmosphere and the vacuum developed inside of the pump will cause a small amount of oil to seep through the end plate and stators into the compression chamber and will thereby provide a means for the lubrication of all of the internal parts of the pump without providing any independent oiling means. The sintered metal also acts as a filter for the oil, removing particulate impurities from the oil as it seeps into the compression chamber. Moreover, the seepage is sufiiciently slow, so that gases occluded in the oil are removed therefrom as the oils pass into the compression chamber. The amount of oil permitted to seep into the internal portion of the pump can be controlled precisely and easily by selecting a sintered metal having an appropriate density and particle size. A part of any desired density and porosity can be manufactured by conventional metal sintering techniques.

An improvement in the construction of the outlet valve employed in the type of pump disclosed by Wessling may also be achieved by the use of sintered metal. The complex valve described by Wessling and the flutter valve assembly shown in LeBlanc U.S. Pat. No. 3,326,456, issued June 20, I967, may be replaced by a simple sintered metal plate, spring mounted over the outlet of the exhaust stage of the pump so as to normally seal the outlet. The sintered metal plate constitutes an inherent valve in that it permits a limited amount ofoil to flow from the oil chamber into the compression chamber during the portion of the pumping cycle when the pressure in the compression chamber is below the pressure immediately outside the outlet. During the exhaust portion of the pump cycle the pressure differential is reversed. and the relatively greater pressure inside the pump forces the plate open to accomplish the exhausting function.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing a pump constructed in accordance with the present invention together with a driving motor;

FIG. 2 is a vertical sectional view through the pump axis;

FIG. 3 is a sectional view taken along line 3-3 in FIG. 2;

FIG. 4 is a sectional view taken along line 4-4 in FIG. 2;

FIG. 5 is a sectional view taken along line 5-5 in FIG. 2;

FIG. 6 is a sectional view taken along line 6-6 in FIG. 2; and

FIG. 7 is a sectional view showing an exhaust valve produced in accordance with the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Although, as described above, the present invention may find application in any type of pump for pumping gases, for exemplary purposes, the invention will be described in the context of an oil immersed, rotary, internal vane type mechanical vacuum pump.

Referring now to the drawings, a pump 10 constructed in accordance with the present invention is shown mounted on a frame 12 and driven by an electric motor 14 through a belt 16. The exterior housing of the pump comprises a casing 18 and an end member 20 (also known as an intake manifold or a trap assembly). End member 20 is provided with an inlet 22, and casing 18 is provided with an exhaust vent 24.

As is usual in vacuum pumps, the inlet 22 is connected to the system to be evacuated, and the air or gas withdrawn from the system is discharged from under the exhaust vent 24. In the following discussion it will be assumed that air is the gas being evacuated.

The internal construction of the pump is shown in the remainder of the figures and particularly in FIG. 2. Extending longitudinally through the pump is a shaft 26, one end of which is journaled in the end member 20 and the other end of which is joumaled in casing 18 at an opening 28. A graphite 0" Ring seal 30, described in detail in applicants copending patent application Ser. No. 779,779, now U.S. Pat. No. 3,525,578 filed Nov. 29, I968 prevents the escape of lubricant through opening 28 along shaft 26. A pulley 32 mounted on the right end of shaft 26 (FIG. 2 orientation) is driven by belt l6 (as shown in FIG. l)v

Two pumping units 34 and 36 are axially aligned on shaft 26 between end member 20 and the end 37 of casing 18. The two pump units are separated by a separator plate 38 and are mounted securely on end member 20 by means of through bolts 40 and end plate 42.

Pumping unit 34 (the intake stage of the pump) comprises a stator d4 (FIG. 4) having a circular opening 46 that is eccentric with respect to the shaft 26. As stated above, stator 44 is held securely to end member 20 by means of through bolts 40. The interior portion of the stator 44 is provided with a recessed inlet 52 that mates with an inlet aperture 54 in the end member 20 (see FIG. 6) and thereby communicates with inlet 22. Stator 44 is also provided with a recessed outlet 56 that mates with hole 58 in separator plate 38, so that expelled air may pass through the separator plate to the exhaust stage of the pump.

Mounted within opening 46 in stator 44 is a cylindrical rotor 48 having flat, smooth end faces, the rotor being in contact with the stator at a terminal point 50, as shown in FIG. 4. Rotor 48 is secured to the shaft by a key 60 and is provided with a pair of opposed radial slots to accommodate radially extending vanes 62 and 64, which are spring-pressed outwardly against the stator by means of coil spring 66. Coil spring 66 is mounted on a radial pin 68 that extends through an opening 70 in shaft 26 (see FIG. 2).

The pumping unit 36 (Le, the exhaust stage of the pump 10) is shown in FIG. 3 and is substantially identical to pumping unit 34 described above, except that stator 72 is rotated counterclockwise 90 relative to stator 44 so that its inlet 74 mates with outlet 56 of the primary stage of the pump and opening 58 in separator plate 38. A recessed outlet 76 is formed in stator 72, and this outlet is in fluid communication with an exhaust port 78 in stator 72 that leads to exhaust vent 24. As in the intake stage, stator 72 is provided with a circular opening 80 that is eccentric with respect to shaft 26, and a cylindrical rotor 82 is secured to the shaft 26 within opening 80 by a key 83. Rotor 82 contacts the stator at a terminal point 84, as shown in FIG. 3. Rotor 82 also has a pair of opposed radial slots that are adapted to accommodate slidably mounted vanes 86 and 88, which are pressed outwardly against the stator by a spring 90 that rides on a pin 92.

As described above, separator plate 38 is provided with a hole 58 connecting the outlet of the intake stage to the inlet of the secondary stage of the pump. Separator plate 38 is also provided with a recessed oil groove 94 and a hole 96 therethrough for the passage of oil (see FIG. 5).

In addition to providing an inlet 22 with inlet aperture 54 leading to the intake stage of the pump, end member also provides a gas ballast valve 100 and an opening 102 covered with a plastic cap 104 for checking the oil level within the casing without disassembling the pump.

End plate 42 provides a means by which the right-hand side of the exhaust stage of the pump (FIG. 2 orientation) may be closed and also provides a means by which the two stages of the pump and separator plate 38 may be held securely to end member 20. Shaft 26 is held in a fixed longitudinal position relative to end plate 42 by retaining rings 103 and thrust washers 105.

In the normal operation of the pump 10, the space between the pump units 34 and 36 and casing 18 is filled with a suitable lubricant, such as oil, up to the level ofinspection opening 102 in end member 20, so that the pumping units are completely immersed. In order to prevent the oil from flooding into the system through the pump outlet or exhaust port 78, an exhaust valve 106 is provided at the outlet. Either of the valves shown in the above-identified Wessling or LeBlanc patents may be used in the pump, but in accordance with the present invention, a new valve has been developed. As shown in FIG. 7, the exhaust valve comprises a thin, sintered metal plate 109 mounted at one end on stator 72 by means of a spring steel plate 107 held in place by a machine screw 108 or other suitable fastening means, so that plate I09 normally completely covers the outlet to exhaust port 78. During the portion of the operating cycle of the pump when the pressure in the pressure chamber is above the atmospheric pressure outside exhaust valve 106 (i.e., when a rotating vane is approaching the out let), air in the compression chamber forces plate 109 away from port 78 and gas bubbles through the oil and passes out of the pump through exhaust vent 24. However, during the portion of the pumping cycle when the pressure in the compression chamber is below atmospheric pressure (i.e., just after a rotating vane has passed the outlet), the plate 109 tightly covers port 78, but, due to its porosity, the pressure differential causes oil in the casing to seep through the plate and into the stator and thereby provide lubrication for the internal working parts. The simplicity and effectiveness of the exhaust valve of the present invention provides a distinct advantage over the more complex valves that have heretofore been used.

In accordance with the present invention, at least one and preferably all of the principal parts of the pump units are formed of sintered metal, rather than the metal castings commonly employed in similar types of pumps. In the preferred embodiment of the present invention, all of the external parts of the pump units, namely, stators 44 and 72 and end plate 42 are formed of sintered metal and thus form a porous matrix through which oil may pass into the internal parts of the pump, thereby eliminating the necessity for separate oil channels in the pump. These parts not only have the proper porosity for lubrication, but they possess adequate tensile strength, ductility and hardness for their designated uses. As the oil slowly seeps through the pump parts from the oil bath into the hollow pump interior, the oil is degassed, thereby removing occluded gases. In this manner, the pumps intake stage may be directly oiled without difficulty. Also, the use of sintered metal parts eliminates the complex degassing arrangements employed in prior art pumps.

Similarly, the preferred embodiment of the present invention employs a sintered metal separator plate 38 between the two pump units 34 and 36. In addition to the advantages of weight and economy inherent in all sintered metal parts used in the subject invention, the separator plate provides an inherent oil passageway from the exhaust to the intake stage and thus insures that an adequate supply of lubrication will reach the intake stage even though hole 96 in center plate 38 may become clogged with impurities. An additional feature of the porous sintered metal separator plate is that oil passing through the plate is filtered thereby, and all particulate impurities in the oil will be removed by the center plate, so that only clean oil will seep through to the intake stage. This advantage of course is also achieved in the sintered metal stators and end plate described above.

The present invention preferably also employs sintered metal rotors 48 and 82 instead of the normal cast iron rotors used in the prior art devices. The main advantage achieved by forming the rotors from sintered metal is in the lightness and inexpensiveness of the parts, especially because of the fact that the end faces of the rotor (i.e., the faces adjacent to the end plate and the center plate) and the outer cylinder walls require close tolerances in order to insure an airtight seal between the rotors and the stators and the plates. The machining required for cast rotors adds a good deal of additional expense to the item, whereas, little or no machining is required for sintered metal parts, because the parts are accurately formed and are highly polished by the dies in which they are manufactured. Moreover, certain lubrication advantages are achieved by manufacturing the rotors from sintered metal. Some of the oil seeping into the compression chambers will naturally come in contact with the rotors and will be absorbed into the porous surfaces of the rotors. This oil will then be available to lubricate the slots of the rotors that come in contact with the slidable vanes and thus will insure an airtight seal between the rotors and the vanes and will also insure that the vanes will be easily slidable in their slots.

The preferred embodiment employs stators, rotors, an end plate, and a separator plate formed from iron particles, substantially all of which are less than I00 microns particle size. The sintered metal in the stators, rotors, and separator plate has a density of about 5.6-7.0 grams per cubic centimeter, compared with a density of ordinary cast iron which may be between 7.0 and 7.8 grams per cubic centimeter (usually about 7.4 grams per cubic centimeter), depending upon the type of cast iron selected. Ideally, the sintered iron employed in these parts has a density of approximately 6.2 grams per cubic centimeter.

The end plate also may be formed from sintered metal having the same density as the stators, but, preferably, this part is formed from sintered metal having a density of about 5.0-6.2 grams per cubic centimeter.

The advantages of the present invention may be achieved with pump parts fonned of substantially any sintered metal. However, because of their wide availability and their structural properties, sintered ferrous metals, especially sintered iron, are the preferred metals for use in practicing the present invention.

Since the vanes are subject to more stress than any other parts in the pump, it was thought that the poor tensile strength and the lack of ductility of sintered metals would render these metals unsatisfactory for use in vanes. But such is not the case, and indeed, sintered metals are not only satisfactory for use in vanes but they provide independent and additional advantages over normal cast iron parts. As in the rotors, sintered metal vanes pick up a certain amount of oil from the compression chamber, and this oil flows by means of capillary action to the inner ends of the vanes and provides additional lubrication between the vanes and the slots in the rotors. Also, the inherent capacity of the vanes to store oil within their porous matrix will insure that there will always be a supply of oil available for the outer ends of the vanes contacting the stators, even though, through some malfunction in the machine, the supply of oil from the stator may be temporarily cut off. Additionally, by using sintered metal parts for the vanes, the desired hardness of the vanes relative to the hardness of the stator may be easily achieved. In the preferred embodiment, the vanes are formed of iron particles, substantially all of which are less than microns particle size, and having a density of between 5.0 and 6.2 grams per cubic centimeter. Ideally, the vanes have a density of 5.8 grams per cubic centimeter. Such a vane is sufiiciently soft to provide proper seating" of the vane in the irregularities of the stator, without the unnecessarily fast wearing out of the vane and without unnecessary wear on the stator. The density and hardness of sintered metal parts may be controlled easily through conventional metal sintering techniques, and the expense involved is minor relative to the cost and difficulty involved in properly heat treating cast metals.

The operation of the pump of the subject invention may be described as follows. inlet 22 is connected to the system to be evacuated, and electric motor 14 is actuated through a suitable electrical source. This results in a clockwise rotation of shaft 26 and the attached rotors 48 and 82 within stators 44 and 72, respectively. ln FIG. 4, vane 64 has just passed intake 52 and has formed a sealed chamber between vane 64 and terminal point 50. As vane 64 continues to rotate until the vane is extending horizontally to the left (according to the FIG. 4 orientation), an increasing vacuum is produced in the sealed chamber, and this causes the air in the system being evacuated to rush into inlet 22, through the inlet aperture 54, and into opening 46 through inlet 52.

After vane 64 passes the position where it extends horizontally to the left, it commences to compress the air in a second sealed chamber formed between vane 64 and terminal point 50 on the upper half of the rotor. As the rotor continues to rotate in a clockwise direction, the volume of this chamber decreases rapidly, so that any air in that chamber becomes compressed. When the pressure in this chamber exceeds the pressure of the air at the inlet of the secondary stage of the pump, the air is forced through outlet 56, through hole 58, and into inlet 74 of the secondary stage of the pump.

The same operation occurs in the secondary stage of the pump. Air compressed in the secondary stage is expelled through outlet 76 and into exhaust port 78. The air then passes through sintered metal exhaust valve 106, bubbles through the oil inside casing 18, and passes out of the casing through exhaust vent 24.

The above-described embodiment, of course, is only an exemplary and preferred construction of the present invention, and it is believed that the present invention can be employed advantageously in any type of pump for pumping gases, as well as the rotary vane type pump described herein.

lclaim:

1. In a two-stage, mechanical vacuum pump comprising a casing providing an inlet and an outlet and being partially filled with oil, primary and secondary pumping units at least partially immersed in the oil and arranged side-by-side in said casing with a separator plate member interposed between them, each of the pumping units having a stator member and a rotor member eccentrically mounted therein and with each of the rotor members having slidable vane members bearing against the inner wall of the cooperating stator member, each of said stator members having an inlet port and an exhaust port, the improvement wherein:

the stator members are formed of sintered metal and possess a porosity sufficient to permit oil to seep through the stator members into the interior of the pumping units, thereby providing lubrication for the interior parts of the pumping units;

the vane members are formed of a sintered metal; and

the stator members are formed of a sintered metal that is harder than the sintered metal used for said vane members.

2. An improvement, as claimed in claim I, wherein:

the sintered metal employed for the vane members is a ferrous metal having a density of about 5.0-6.2 grams per cubic centimeter; and

the sintered metal employed for the stator members is the same ferrous metal having a density of about 5.6-7.0 grams per cubic centimeter.

3. In a two-stage, mechanical vacuum pump comprising a casing providing an inlet and an outlet and being partially filled with oil. primary and secondaq pumping units at least partially immersed in the oil and arranged side-by-side in said casing with a separator plate member interposed between them, each of the pumping units having a stator member and a rotor member eccentrically mounted therein and with each of the rotor members having slidable vane members bearing against the inner wall of the cooperating stator member, each of said stator members having an inlet port and an exhaust port, the improvement wherein:

the stator members are formed of sintered metal and possess a porosity sufficient to permit oil to seep through the stator members into the interior of the pumping units, thereby providing lubrication for the interior parts of the pumping units; and

all of the members are formed of sintered ferrous metal, the

vane member having a density of about 5.0-6.2 grams per cubic centimeter, and the stator, rotor, and separator plate members being harder than the vane member and having a density of about 5.6-7.0 grams per cubic centimeter.

4. An improvement, as claimed in claim 3, wherein the exhaust port of the secondary pumping unit is positioned below the level of the oil in the casing, and a sintered metal exhaust valve covers the exhaust port, said exhaust valve comprising a sintered metal plate spring-mounted over the exhaust port, said exhaust valve having a porosity sufficient to permit the oil in said casing surrounding the pumping units to seep through said exhaust valve into the interior portion of said pumping units when the pressure within the exhaust port is less than the pressure outside of said exhaust port.

5. in a vacuum pump comprising a hollow casing at least partially filled with oil and a pumping unit mounted in said hollow casing so as to be at least partially immersed in oil, said pumping unit comprising a stator having an open interior portion, a rotor eccentrically mounted in said interior portion, and at least one vane extending radially from the rotor into contact with the interior wall of the stator, an improvement wherein:

the stator is formed of sintered metal having a porosity sufficient to permit oil in the hollow casing to seep through the stator into the interior portion of the stator, thereby providing internal lubrication for the pump; and

the vane is formed of a porous sintered metal that is softer than the sintered metal of which the stator is formed, whereby friction between the stator and vane will cause the more easily replaced vane to wear down rather than the stator.

6. An improvement as claimed in claim 5 wherein:

the rotor is formed of sintered metal;

the stator is formed from sintered metal particles, substantially all of which are less than about microns particle size, and the stator has a density of about 5.6-7.0 grams per cubic centimeter; and

the vane is formed from sintered metal particles, substantially all of which are less than about 100 microns particle size, and the vane has a density of about 5.0-6.2 grams per cubic centimeter.

7. In a vacuum pump comprising a hollow casing at least partially filled with oil and a pumping unit mounted in said hollow casing so as to be at least partially immersed in oil, said pumping unit comprising a stator having an open interior portion, a rotor eccentrically mounted in said interior portion, and at least one vane extending radially from the rotor into contact with the interior wall of the stator, an improvement wherein the stator is formed of sintered metal having a porosity sufficient to permit oil in the hollow casing to seep through the stator into the interior portion of the stator, thereby providing internal lubrication for the pump, and comprises an outlet positioned below the level of the oil in the hollow casing, an exhaust valve being mounted over said outlet, said exhaust valve comprising a spring-mounted porous sintered metal plate having a porosity sufficient to permit oil in the casing to seep through the sintered metal plate and into the interior portion of the pump whenever the pressure inside the outlet is relatively lower than the pressure immediately outside the outlet.

8. An improvement as claimed in claim 7 wherein the reciprocable internal compression member comprises a rotor eccentrically mounted in said interior portion and at least one vane that extends radially from the rotor into contact with the interior wall of the stator, with the vane being formed of a sintered metal that is softer than the sintered metal from which the stator is formed, so that friction between the vane and the stator will cause the vane to wear down rather than the stator.

9 An improvement as claimed in claim 8 wherein:

the rotor and stator are formed of sintered ferrous metal having a density of about 5.6-7.0 grams per cubic centimeter; and

the vanes are formed of sintered ferrous metal having a density of about 5.0-6.2 grams per cubic centimeter.

l0. ln a two-stage mechanical vacuum pump comprising a hollow casing at least partially filled with oil, primary and secondary pumping units arranged side-by-side in the hollow casing with a separator plate interposed between them, said pumping units being at least partially immersed in the oil and each said pumping unit comprising a stator having a cylindrical opening therein, a rotor mounted eccentrically in said cylindrical opening, and vanes extending radially from the rotor into contact with the wall of the cylindrical opening in the stator, the cylindrical opening in the secondary pumping unit having an open end that is covered by an end plate, and the secondary pumping unit having an outlet positioned below the level of oil in the hollow casing and having an exhaust valve mounted thereon, an improvement wherein:

the stators, rotors, and separator plate are formed of sintered ferrous metal having a density of about 5.6 to 7.0 grams per cubic centimeter and having a porosity suffcient to permit oil to seep through the sintered metal; the vanes and end plate are formed of sintered ferrous metal having a density of about 5.0-6.2 grams per cubic centimeter and having a porosity sufficient to permit oil to seep through the sintered metal; and the exhaust valve comprises a spring-mounted plate positioned over the outlet of the secondary pumping unit, said plate being formed of sintered metal having a porosity sufficient to permit oil in the hollow casing to seep through the plate and into the interior of the secondary pumping unit whenever the pressure inside the outlet is less than the pressure outside the outlet.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 2 699 954 Dated November 23 1971 Inventofls) Joseph A. LeBlanc. Jr.

It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 2, line 26, delete "sufficient" and substitute therefor -insufficient-.

Claim 8, Column 9, line 3, delete "An improvement as claimed in claim 7 wherein" and insert -In a mechanical vacuum pump comprising a stator having walls and an open interior portion, a reciprocable internal compression member mounted in said open interior portion, and a source of liquid lubricant outside the stator, an improvement wherein:

the stator is formed of a porous sintered metal having a porosity sufficient to permit the liquid lubricant to seep through the walls of the stator and into the open interior portion thereof, thereby providing lubrication for the internal parts of the pump; and-.

Signed and sealed this 9th day of May 1972.

(SEAL) A ttes t:

EDWARD II.FLETCHEI L,J.R. ROBERT GOTTSCHALK A ates ting; Officer Commissioner of Patents "ORM F'O-1050 10-69) I uscoMM-oc 50376-F'BD a U 5 GOVERNMENT PRINTING OFFICE I9, D36-33l 

1. In a two-stage, mechanical vacuum pump comprising a casing providing an inlet and an outlet and being partially filled with oil, primary and secondary pumping units at least partially immersed in the oil and arranged side-by-side in said casing with a separator plate member interposed between them, each of the pumping units having a stator member and a rotor member eccentrically mounted therein and with each of the rotor members having slidable vane members bearing against the inner wall of the cooperating stator member, each of said stator members having an inlet port and an exhaust port, the improvement wherein: the stator members are formed of sintered metal and possess a porosity sufficient to permit oil to seep through the stator members into the interior of the pumping units, thereby providing lubrication for the interior parts of the pumping units; the vane members are formed of a sintered metal; and the stator members are formed of a sintered metal that is harder than the sintered metal used for said vane members.
 2. An improvement, as claimed in claim 1, wherein: the sintered metal employed for the vane members is a ferrous metal having a density of about 5.0-6.2 grams per cubic centimeter; and the sintered metal employed for the stator members is the same ferrous metal having a density of about 5.6-7.0 grams per cubic centimeter.
 3. In a two-stage, mechanical vacuum pump comprising a casing providing an inlet and an outlet and being partially filled with oil, primary and secondary pumping units at least partially immersed in the oil and arranged side-by-side in said casing with a separator plate member interposed between them, each of the pumping units having a stator member and a rotor member eccentrically mounted therein and with each of the rotor members having slidable vane members bearing against the inner wall of the cooperating stator member, each of said stator members having an inlet port and an exhaust port, the improvement wherein: the stator members are formed of sintered metal and possess a porosity sufficient to permit oil to seep through the stator members into the interior of the pumping units, thereby providing lubrication for the interior parts of the pumping units; and all of the members are formed of sintered ferrous metal, the vane member having a density of about 5.0-6.2 grams per cubic centimeter, and the stator, rotor, and separator plate members being harder than the vane member and having a density of about 5.6-7.0 grams per cubic centimeter.
 4. An improvement, as claimed in claim 3, wherein the exhaust port of the secondary pumping unit is positioned below the level of the oil in the casing, and a sintered metal exhaust valve covers the exhaust port, said exhaust valve comprising a sintered metal plate spring-mounted over the exhaust port, said exhaust valve having a porosity sufficient to permit the oil in said casing surrounding the pumping units to seep through said exhaust valve into the interior portion of said pumping units when the pressure within the exhaust port is less than the pressure outside of said exhaust port.
 5. In a vacuum pump comprising a hollow casing at least partially filled with oil and a pumping unit mounted in said hollow casing so as to be at least partially immersed in oil, said pumping unit comprising a stator having an open interior portion, a rotor eccentrically mounted in said interior portion, and at least one vane extending radially from the rotor into contact with the interior wall of the stator, an improvement wherein: the stator is formed of sintered metal having a porosity sufficient to permit oil in the hollow casing to seep through the stator into the interior portion of the stator, thereby providing internal lubrication for the pump; and the vane is formed of a porous sintered metal that is softer than the sintered metal of which the stator is formed, whereby friction between the stator and vane will cause the more easily replaced vane to wear down rather than the stator.
 6. An improvement as claimed in claim 5 wherein: the rotor is formed of sintered metal; the stator is formed from sintered metal particles, substantially all of which are less than about 100 microns particle size, and the stator has a density of about 5.6-7.0 grams per cubic centimeter; and the vane is formed from sintered metal particles, substantially all of which are less than about 100 microns particle size, and the vane has a density of about 5.0-6.2 grams per cubic centimeter.
 7. In a vacuum pump comprising a hollow casing at least partially filled with oil and a pumping unit mounted in said hollow casing so as to be at least partially immersed in oil, said pumping unit comprising a stator having an open interior portion, a rotor eccentrically mounted in said interior portion, and at least one vane extending radially from the rotor into contact with the interior wall of the stator, an improvement wherein the stator is formed of sintered metal having a porosity sufficient to permit oil in the hollow casing to seep through the stator into the interior portion of the stator, thereby providing internal lubrication for the pump, and comprises an outlet positioned below the level of the oil in the hollow casing, an exhaust valve being mounted over said outlet, said exhaust valve comprising a spring-mounted porous sintered metal plate having a porosity sufficient to permit oil in the casing to seep through the sintered metal plate and into the interior portion of the pump whenever the pressure inside the outlet is relatively lower than the pressure immediately outside the outlet.
 8. An improvement as claimed in claim 7 wherein the reciprocable internal compression member comprises a rotor eccentrically mounted in said interior portion and at least one vane that extends radially from the rotor into contact with the interior wall of the stator, with the vane being formed of a sintered metal that is softer than the sintered metal from which the stator is formed, so that friction between the vane and the stator will cause the vane to wear down rather than the stator.
 9. An improvement as claimed in claim 8 wherein: the rotor and stator are formed of sintered ferrous metal having a density of about 5.6-7.0 grams per cubic centimeter; and the vanes are formed of sintered ferrous metal having a density of about 5.0-6.2 grams per cubic centimeter.
 10. In a two-stage mechanical vacuum pump comprising a hollow casing at least partially filled with oil, primary and secondary pumping units arranged side-by-side in the hollow casing with a separator plate interposed between them, said pumping units being at least partially immersed in the oil and each said pumping unit comprising a stator having a cylindrical opening therein, a rotor mounted eccentrically in said cylindrical opening, and vanes extending radially from the rotor into contact with the wall of the cylindrical opening in the stator, the cylindrical opening in the secondary pumping unit having an open end that is covered by an end plate, and the secondary pumping unit having an outlet positioned below the level of oil in the hollow casing and having an exhaust valve mounted thereon, an improvement wherein: the stators, rotors, and separator plate are formed of sintered ferrous metal having a density of about 5.6 to 7.0 grams per cubic centimeter and having a porosity sufficient to permit oil to seep through the sintered metal; the vanes and end plate are formed of sintered ferrous metal having a density of about 5.0-6.2 grams per cubic centimeter and having a porosity sufficient to permit oil to seep through the sintered metal; and the exhaust valve comprises a spring-mounted plate positioned over the outlet of the secondary pumping unit, said plate being formed of sintered metal having a porosity sufficient to permit oil in the hollow casing to seep through the plate and into the interior of the secondary pumping unit whenever the pressure inside the outlet is less than the pressure outside the outlet. 